clk: ti: omap36xx: Work around sprz319 advisory 2.1

The OMAP36xx DPLL5, driving EHCI USB, can be subject to a long-term
frequency drift. The frequency drift magnitude depends on the VCO update
rate, which is inversely proportional to the PLL divider. The kernel
DPLL configuration code results in a high value for the divider, leading
to a long term drift high enough to cause USB transmission errors. In
the worst case the USB PHY's ULPI interface can stop responding,
breaking USB operation completely. This manifests itself on the
Beagleboard xM by the LAN9514 reporting 'Cannot enable port 2. Maybe the
cable is bad?' in the kernel log.

Errata sprz319 advisory 2.1 documents PLL values that minimize the
drift. Use them automatically when DPLL5 is used for USB operation,
which we detect based on the requested clock rate. The clock framework
will still compute the PLL parameters and resulting rate as usual, but
the PLL M and N values will then be overridden. This can result in the
effective clock rate being slightly different than the rate cached by
the clock framework, but won't cause any adverse effect to USB
operation.

Signed-off-by: Richard Watts <rrw@kynesim.co.uk>
[Upported from v3.2 to v4.9]
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Ladislav Michl <ladis@linux-mips.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/clk/ti/clock.h b/drivers/clk/ti/clock.h
index 90f3f472ae1c..13c37f48d9d6 100644
--- a/drivers/clk/ti/clock.h
+++ b/drivers/clk/ti/clock.h
@@ -257,11 +257,20 @@ long omap2_dpll_round_rate(struct clk_hw *hw, unsigned long target_rate,
 unsigned long omap3_clkoutx2_recalc(struct clk_hw *hw,
 				    unsigned long parent_rate);
 
+/*
+ * OMAP3_DPLL5_FREQ_FOR_USBHOST: USBHOST and USBTLL are the only clocks
+ * that are sourced by DPLL5, and both of these require this clock
+ * to be at 120 MHz for proper operation.
+ */
+#define OMAP3_DPLL5_FREQ_FOR_USBHOST	120000000
+
 unsigned long omap3_dpll_recalc(struct clk_hw *hw, unsigned long parent_rate);
 int omap3_dpll4_set_rate(struct clk_hw *clk, unsigned long rate,
 			 unsigned long parent_rate);
 int omap3_dpll4_set_rate_and_parent(struct clk_hw *hw, unsigned long rate,
 				    unsigned long parent_rate, u8 index);
+int omap3_dpll5_set_rate(struct clk_hw *hw, unsigned long rate,
+			 unsigned long parent_rate);
 void omap3_clk_lock_dpll5(void);
 
 unsigned long omap4_dpll_regm4xen_recalc(struct clk_hw *hw,